Gas-electric propulsion system for an aircraft

ABSTRACT

In one aspect the present subject matter is directed to a gas-electric propulsion system for an aircraft. The system may include a turbofan jet engine, an electric powered boundary layer ingestion fan that is coupled to a fuselage portion of the aircraft aft of the turbofan jet engine, and an electric generator that is electronically coupled to the turbofan jet engine and to the boundary layer ingestion fan. The electric generator converts rotational energy from the turbofan jet engine to electrical energy and provides at least a portion of the electrical energy to the boundary layer ingestion fan. In another aspect of the present subject matter, a method for propelling an aircraft via the gas-electric propulsion system is disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This non-provisional application claims the benefit of priority under 35U.S.C. § 119(e) to U.S. Provisional Patent Application No. 62/107,196,entitled “GAS-ELECTRIC PROPULSION SYSTEM FOR AN AIRCRAFT”, filed Jan.23, 2015, which is herein incorporated in its entirety by reference.

FIELD OF THE INVENTION

The present subject matter relates generally to a gas-electricpropulsion system for an aircraft. More particularly, the presentsubject matter relates to a gas-electric propulsion system that convertsrotational energy from a gas powered aircraft engine into electricenergy via a low pressure (LP) and/or a high pressure (HP) electricgenerator to drive an electric powered boundary layer ingestion fan.

BACKGROUND OF THE INVENTION

A conventional commercial aircraft has a fuselage (tube) and wingconfiguration, and a propulsion system that provides thrust. Thepropulsion system generally includes two or more jet engines such asturbofans. The jet engines may be mounted to the aircraft in a varietyof ways. For example, the jet engines may be suspended beneath the wing,blended with the wing or mounted directly to the fuselage. The jetengines are typically installed at a distance from the fuselage and/orthe wing, such that the jet engines and the fuselage interact withseparate freestream airflows, thus reducing turbulence of air enteringan inlet portion of the jet engine. The net propulsive thrust of the jetengines is directly proportional to the difference between jet engineexhaust velocity and freestream velocity of the air approaching theengine while in motion.

Drag, such as skin friction, form and induced drag have a direct effecton net propulsive thrust of the propulsion system. Total aircraft dragis generally proportional to a difference between freestream velocity ofair approaching the aircraft and an average velocity of a wakedownstream from the aircraft and that is produced due to the drag on theaircraft. Various parameters of the jet engine such as jet enginediameter, thrust capability, fan pressure ratio (FPR) for a turbofan jetengine and/or jet engine exhaust velocity must be sized and/or designedto accommodate for the total aircraft drag.

Systems and/or technics have been proposed to counter the effects ofdrag and/or to improve efficiency of the jet engine. For example,various propulsion systems incorporate boundary layer ingestion systemssuch as one or more boundary layer ingestion fan(s) and/or relatedtechniques that route a portion of relatively slow moving air whichforms a boundary layer across the fuselage into the jet engine at orupstream from a fan section of the jet engine. While this techniquereduces the net drag by re-energizing the boundary layer downstream fromthe aircraft, the flow of air from the boundary layer entering the jetengine generally has a non-uniform or distorted velocity profile. As aresult, conventional turbofan jet engines, particularly those turbofansmounted under-wing, may experience loss of operability or efficiency,thus minimizing or negating the benefits of reduced drag on theaircraft.

Accordingly, a gas-electric propulsion system that reduces net drag onthe aircraft while increasing overall propulsion system efficiencyand/or that allows for reduced engine diameter and/or fan pressure ratiofor wing-mounted turbofans would be welcomed in the technology.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

In one aspect, the present subject matter is directed to a gas-electricpropulsion system for an aircraft. The system includes a pair of jetengines suspended beneath a wing of the aircraft, an electric poweredboundary layer ingestion fan coupled to a fuselage portion of theaircraft aft of the wing, and an electric generator that iselectronically coupled to the pair of jet engines and to the boundarylayer ingestion fan. The electric generator converts rotational energyfrom at least one jet engine of the pair of j et engines to electricalenergy and provides at least a portion of the electrical energy to theboundary layer ingestion fan.

In another aspect, the present subject matter is directed to agas-electric propulsion system for an aircraft. The system may include aturbofan jet engine, an electric powered boundary layer ingestion fancoupled to a fuselage portion of the aircraft aft of the turbofan jetengine, and an electric generator that is electronically coupled to theturbofan jet engine and to the boundary layer ingestion fan. Theelectric generator converts rotational energy from the turbofan jetengine to electrical energy and provides at least a portion of theelectrical energy to the boundary layer ingestion fan.

In a further aspect, the present subject matter is directed to a methodfor propelling an aircraft via a gas-electric propulsion system. Themethod includes providing electrical energy from an energy storagedevice to an electric motor of a boundary layer ingestion fan where theboundary layer ingestion fan is mounted to the aircraft aft of a wing ofthe aircraft. The method further includes engaging an electric motor ofthe boundary layer ingestion fan to produce thrust sufficient to propelthe aircraft.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appendedfigures, in which:

FIG. 1 is a top view of an exemplary aircraft as may incorporate variousembodiments of the present invention;

FIG. 2 is a port side view of the aircraft as illustrated in FIG. 1;

FIG. 3 is a schematic cross-sectional view of an exemplary high-bypassturbofan jet engine according to various embodiments of the presentsubject matter;

FIG. 4 is a schematic cross-sectional side view of an exemplary boundarylayer ingestion (BLI) fan according to various embodiments of thepresent subject matter;

FIG. 5 is a schematic view of an exemplary gas-electric propulsionsystem, according to various embodiments of the present invention; and

FIG. 6 is a flow diagram of an exemplary method for propelling anaircraft via a gas-electric propulsion system as shown in FIG. 5,according to various embodiment of the present subject matter.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to present embodiments of theinvention, one or more examples of which are illustrated in theaccompanying drawings. The detailed description uses numerical andletter designations to refer to features in the drawings. Like orsimilar designations in the drawings and description have been used torefer to like or similar parts of the invention. As used herein, theterms “first”, “second”, and “third” may be used interchangeably todistinguish one component from another and are not intended to signifylocation or importance of the individual components. The terms“upstream” and “downstream” refer to the relative direction with respectto fluid flow in a fluid pathway. For example, “upstream” refers to thedirection from which the fluid flows, and “downstream” refers to thedirection to which the fluid flows.

In general, the present subject matter is directed to a gas-electricpropulsion system for an aircraft such as but not limited to aconventional commercial aircraft. In various embodiments, thegas-electric propulsion system includes one or more jet engines such asturbofan engines (variable or fixed pitch, ducted or non-ducted, gearedor direct drive) that utilize high pressure (HP) generators, lowpressure (LP) generators, or any combination of (HP) and (LP) generatorsto distribute electric power generated by the turbofan engines to one ormore electric powered Boundary Layer Ingestion (BLI) fan(s). Inparticular embodiments, energy storage devices such as batterieselectronically coupled to the (LP) and/or (HP) generators may be used toaid in driving the BLI fan, thus providing thrust to the aircraft duringparticular operational modes.

In various embodiments, the BLI fan is sized to ingest a boundary layerof air flowing over the fuselage of the aircraft during flight, therebyreducing aircraft drag and enabling propulsive efficiency increases. Inaddition or in the alternative, the BLI fan may be used to generateadditional thrust for the aircraft while in flight such as duringtakeoff, cruise and decent. As a result, the additional thrust incombination with reduced drag may afford a decrease in diameter and/orfan pressure ratio of the wing-mounted turbofans, thus increasingpropulsive efficiency by reducing fuel burn. In addition or in thealternative, a decrease in diameter of the wing-mounted turbofans mayminimalize engine induced drag, thus further contributing to propulsiveefficiency gains. In addition or in the alternative, the BLI fan maygenerate sufficient thrust to move the aircraft on the ground such asduring taxi, thus reducing overall jet engine fuel burn.

Referring now to the drawings, wherein identical numerals indicate thesame elements throughout the figures, FIG. 1 provides a top view of anexemplary aircraft 10 as may incorporate various embodiments of thepresent invention. FIG. 2 provides a port side view of the aircraft 10as illustrated in FIG. 1. As shown in FIGS. 1 and 2 collectively, theaircraft 10 includes a fuselage 12 having a longitudinal centerline 14that extends therethrough. The fuselage 12 extends longitudinallybetween a forward or nose section 16 and an aft or tail section 18 ofthe aircraft 10. The aircraft 10 further includes a wing 20 that extendslaterally outwardly with respect to the longitudinal centerline 14 froma port side 22 and from a starboard side 24 (FIG. 1) of the fuselage 12.The fuselage 12 includes an outer surface or skin 26.

In various embodiments, as shown in FIG. 1, the aircraft 10 includes agas-electric propulsion system 100, herein referred to as “system 100”.The system 100 includes a pair of jet engines 102, 104 suspended beneaththe wing(s) 20 in an under-wing configuration and at least one BoundaryLayer Ingestion (BLI) fan 106 mounted to the aircraft 10 aft of the wing20 and/or the jet engines 102, 104. The BLI fan 106 may be fixedlyconnected to the fuselage 12 at any point that is aft from the wing 20and/or the jet engines 102, 104. For example, in particular embodiments,as shown in FIGS. 1 and 2, the BLI fan 106 may be fixedly connected tothe fuselage aft of the tail section 18. However, it should beappreciated that in alternate embodiments, the BLI fan 106 may bepositioned forward of the tail section 18 or may be incorporated into orblended with the tail section 18.

In various embodiments, the jet engines 102, 104 are high-bypassturbofan jet engines. FIG. 3 is a schematic cross-sectional view of anexemplary high-bypass turbofan jet engine 200 herein referred to as“turbofan 200” and in various embodiments, may be representative of jetengines 102, 104. As shown in FIG. 3, the turbofan 200 has alongitudinal or axial centerline axis 202 that extends therethrough forreference purposes. In general, the turbofan 200 may include a fansection 204 and a gas-powered core turbine engine 206 disposeddownstream from the fan section 204.

The core turbine engine 206 may generally include a substantiallytubular outer casing 208 that defines an annular inlet 210. The outercasing 208 encases, in serial flow relationship, a booster or lowpressure (LP) compressor 212, a high pressure (HP) compressor 214, acombustion section 216, a high pressure (HP) turbine 218, a low pressure(LP) turbine 220 and a jet exhaust section 222. A high pressure (HP)shaft or spool 224 drivingly connects the HP turbine 218 to the HPcompressor 214 and a low pressure (LP) shaft or spool 226 drivinglyconnects the LP turbine 220 to the LP compressor 212. The (LP) shaft orspool 226 may also be connected to a fan spool or shaft 228 of the fansection 204. In particular embodiments, as shown in FIG. 3, the (LP)shaft or spool 226 may be connected directly to the fan spool 228 suchas in a direct-drive configuration. In alternative embodiments, as shownin FIG. 5 and described in more detail below, the (LP) shaft or spool226 may be connected to the fan spool 228 via a reduction gear 230 suchas in an indirect-drive or geared-drive configuration.

As shown in FIG. 3, the fan section 204 includes a plurality of fanblades 232 that are coupled to and that extend radially outwardly fromthe fan spool 228. An annular fan casing or nacelle 234circumferentially surrounds the fan section 204. It should beappreciated by those of ordinary skill in the art that the nacelle 234may be configured to be supported relative to the core turbine engine206 by a plurality of circumferentially-spaced outlet guide vanes 236.Moreover, a downstream section 238 of the nacelle 234 may extend over anouter portion of the core turbine engine 206 so as to define a bypassairflow passage 240.

During operation of the turbofan 200, a volume of air 242 enters theturbofan 200 through an associated inlet 244 of the nacelle 234 and/orfan section 204 at a freestream velocity FSVi. The volume of air 242then passes through the fan blades 232 and is split into a first volumeof air as indicated by arrow 246 that moves through the bypass airflowpassage 240 and a second volume of air indicated by arrow 248 whichenters the booster or LP compressor 212. The ratio between the firstvolume of air 246 and the second volume of air 248 is commonly known asFan Pressure Ration or FPR. The pressure of the second volume of air 248is then increased as it is routed towards the high pressure (HP)compressor 214 (as indicated by arrow 250). The second volume of air 250is routed from the HP compressor 214 into the combustion section 216where it is mixed with fuel and burned to provide combustion gases 252.

The combustion gases 252 are routed through the HP turbine 218 where aportion of thermal and/or kinetic energy from the combustion gases 252is extracted via various stages of HP turbine rotor blades 254 that arecoupled to the HP shaft or spool 224, thus causing the HP shaft or spool224 to rotate, thereby supporting operation of the HP compressor 214.The combustion gases 252 are then routed through the LP turbine 220where a second portion of thermal and kinetic energy is extracted fromthe combustion gases 252 via various stages of LP turbine rotor blades256 that are coupled to the LP shaft or spool 226, thus causing the LPshaft or spool 226 to rotate, thereby supporting operation of the LPcompressor 212 and/or rotation of the fan spool or shaft 228. Thecombustion gases 252 are then routed through jet exhaust nozzle section222 of the core turbine engine 206 to provide a first propulsive thrustT₁ at a first exhaust velocity EV₁ of the turbofan 200. Simultaneously,the pressure of the first volume of air 246 is substantially increasedas the first volume of air 246 is routed through the bypass airflowpassage 240 before it is exhausted therefrom at a second exhaustvelocity EV₂ via a fan nozzle exhaust section 258 of the turbofan 200,thus providing a second propulsive thrust T₂.

FIG. 4 provides a schematic cross-sectional side view of an exemplaryBLI fan 300 and in various embodiments may be representative of BLI fan106. As shown in FIG. 4, the BLI fan 300 has a longitudinal or axialcenterline axis 302 that extends therethrough for reference purposes. Ingeneral, the BLI fan 300 includes an electric motor 304, a rotor shaft306 coupled to the electric motor 304, a plurality of fan blades 308coupled to the rotor shaft 306 and one or more stages of stator orsupport vanes 310. In particular embodiments, the BLI fan 300 mayinclude an outer casing or nacelle 312 and an inner casing 314. A fanduct or flow passage 316 is at least partially defined between thenacelle 312 and the inner casing 314. The outer casing 312 may at leastpartially surround any one or more of the electric motor 304, the rotorshaft 306, the fan blades 308, the stator vanes 310, the inner casing314 or other components of the BLI fan 300. The outer casing 312 atleast partially defines an inlet 318 and an outlet to the fan duct 316.

In various embodiments, the inlet 318 is oriented with respect to thefuselage to ingest at least a portion of a boundary layer flow of airthat is formed along the outer surface or skin 26 (FIGS. 1 and 2) of thefuselage 12 during flight. In particular embodiments, the inlet 318 issized and/or shaped to optimize ingestion of the boundary layer flow ofair. In addition, in various embodiments, the outlet 320 of the fan duct316 is sized and/or shaped to provide maximum rearward thrust from theBLI fan 300, thus supplementing thrust provided by the jet engines 102,104 and/or thereby providing sufficient thrust to independently propelor move the aircraft 10 in flight or while on the ground.

The electric motor 304 may be any electric motor that has a suitablespecific power or weight to power ratio that is suitable for aviationuse and its intended purpose. For example, in various embodiments, theelectric motor 304 may be a superconducting electric motor. Inparticular embodiments, the electric motor 304 may have an efficiency ofgreater than 0.995, an output of approximately 3000 horsepower and aspecific power of approximately 5-6 horsepower per pound weight. Inparticular embodiments, the electric motor 304 may be either a directcurrent (DC) motor or an alternating current (AC) motor.

The fan blades 308 may be formed from any material suitable for use in aflight environment. In particular embodiments, the fan blades 308 are atleast partially formed from a composite material. In particularembodiments, as shown in FIG. 4, the fan blades 308 may include a metalalloy leading edge 322 and/or trailing edge 324. For example, in oneembodiment at least one of the leading edge 322 and the trailing edge324 includes a titanium alloy portion. In particular embodiments, thefan blades 308 may include sculpted features or surfaces 326. Thesculpted features or surfaces 326 of the fan blades 308 may be formed tominimize associated fan blade noise.

In various embodiments, the BLI fan 300 may include at least one stageor row of inlet or stator vanes 328 that extend radially between theinner casing 314 and the fan nacelle 312 within the fan duct or flowpassage 316 upstream from the fan blades 308. In particular embodiments,the stator vanes 328 may be fixed in position. In other embodiments, thestators vanes 326 may be variable or adjustable so as to affect a flowof air and/or the boundary layer air flowing into the inlet 318.

FIG. 5 provides a schematic view of the gas-electric propulsion system100 or system 100, according to various embodiments of the presentinvention. In various embodiments, as shown in FIG. 5, system 100further includes an electric generator 108 coupled to one or both of thejet engines 102, 104 and to the BLI fan 106. In one embodiment, theelectric generator 108 is a low pressure (LP) electric generatorconfigured to convert rotational energy from the LP shaft(s) or spool(s)226 of one or both jet engines of the pair of jet engines 102, 104. Inone embodiment, the electric generator 108 is a high pressure (HP)electric generator that is configured to convert rotational energy fromthe HP shaft(s) or spool(s) 224 of one or both jet engines of the pairof jet engines 102, 104. The electric generator 108 may be a DCgenerator or an AC generator. The electric generator 108 may provideelectric energy to the BLI fan 106 during various flight conditions. Forexample, the electric generator 108 may provide electrical energy to theBLI fan 106 during taxi, take off, cruise, decent and/or landing of theaircraft.

In various embodiments, as shown in FIG. 5, the system 100 may includean energy storage device 110 that is electronically coupled to theelectric generator 108. In particular embodiments, the energy storagedevice 110 includes high capacity batteries. In various embodiments, theenergy storage device 110 is configured to receive and store electricalenergy from the electrical generator 108 and to provide the storedelectrical energy to the BLI fan 106 when required. The energy storagedevice 110 may provide stored electric energy to the BLI fan 106 duringparticular flight conditions. For example, the energy storage device 110may provide electrical energy to the BLI fan 106 during taxi, take off,cruise, decent and/or landing of the aircraft.

In various embodiments, as show in FIG. 5, the system 100 may furtherinclude an energy management system or controller 112. The energymanagement system 112 may be configured or programmed to monitor varioussystem conditions. For example, the energy management system 112 maymonitor energy generation by the electric generator 108, remainingenergy storage capacity of the energy storage device 110, rotationalspeed of the LP shaft(s) or spool(s) 226 and/or the HP shaft(s) orspool(s) 224, etc. . . .

It should also be appreciated that, as used herein, the term “energymanagement system” generally refers to any suitable computing deviceand/or processing unit known in the art. As such, the energy managementsystem 112 described herein may, for example, include one or moreprocessor(s) and associated memory device(s) configured to perform avariety of computer-implemented functions (e.g., performing the variousfunctions described herein). As used herein, the term “processor” refersnot only to integrated circuits referred to in the art as being includedin a computer, but also refers to a controller, a microcontroller, amicrocomputer, a programmable logic controller (PLC), an applicationspecific integrated circuit, and other programmable circuits.

Additionally, the memory device(s) included within a given controllermay generally comprise memory element(s) including, but not limited to,computer readable medium (e.g., random access memory (RAM)), computerreadable non-volatile medium (e.g., a flash memory), a floppy disk, acompact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), adigital versatile disc (DVD) and/or other suitable memory elements. Suchmemory device(s) may generally be configured to store suitablecomputer-readable instructions that, when implemented by theprocessor(s), configure the associated energy management system 112 toperform various functions, such as monitoring energy generation by theelectric generator 108, monitoring and/or calculating remaining energystored in the energy storage device 110, rate of energy consumption bythe BLI fan 106 and other system variables.

It should be appreciated by one of ordinary skill that the variousembodiments described and illustrated herein may provide a method forpropelling the aircraft 10 via the gas-electric propulsion system 100.FIG. 6 provides a flow diagram of an exemplary method 400 for propellingthe aircraft 10 via the gas-electric propulsion system 100. At 402,method 400 includes providing electrical energy from the energy storagedevice 110 to the electric motor 304 of the boundary layer ingestion fan106, 300, wherein the boundary layer ingestion fan 106, 300 is mountedto the aircraft 10 aft of the wing 20. At 404, method 400 includesengaging the electric motor 304 to rotate the fan blades 308 of theboundary layer ingestion fan 106, 300 to produce thrust sufficient topropel the aircraft 10.

In other embodiments, method 400 may further include providingelectrical energy to the energy storage device 110 via electricgenerator 108. Method 400 may include providing electrical energy to theenergy storage device 110 via a high pressure electric generator that iscoupled to the high pressure spool 224 of the turbofan jet engine 200.In one embodiment, method 400 may include providing the electricalenergy to the energy storage device 110 via a low pressure electricgenerator that is coupled to the low pressure spool 226 of the turbofanjet engine 200. In one embodiment, method 400 may include providingadditional thrust to propel the aircraft via one or more of the jetengines 102, 104. In particular embodiments, method 400 may includeproviding electrical energy directly to the boundary layer ingestion fan106, 300 via high pressure electric generator that is coupled to thehigh pressure spool 224 of the turbofan jet engine 200. In particularembodiments, method 400 may include providing electrical energy directlyto the boundary layer ingestion fan 106, 300 via low pressure electricgenerator that is coupled to the low pressure spool 226 of the turbofanjet engine 200.

The gas-electric propulsion system 100 as described herein and asillustrated in the referenced figures provides various technicalbenefits over conventional aircraft propulsion systems. For example, invarious embodiments, the boundary layer ingestion fan decreases theaircrafts drag by re-energizing the fuselage boundary layer, thusenabling reduced thrust requirements for the under-wing turbofans. As aresult, reduced fan pressure ratio at a given turbofan engine diameteris required, thus increasing the propulsive efficiency of the propulsionsystem.

By having a high specific power LP generator and/or high specific powerfan motor 304 in conjunction with the energy storage devices 110, theBLI fan 108 may be used to taxi the aircraft, thus reducing overall fuelburn. In addition or in the alternative, by having a high specific powerHP electric generator and/or fan motor 304, core power extraction may beused to raise the HP compressor operating line at cruise, thus providingincreased overall system efficiency. In addition or in the alternative,the high specific power HP electric generator and/or fan motor 304 mayeliminate a starter/generator typically required for the turbofan jetengines 102, 104, may eliminate a requirement for a Ram Air Turbine(RAT), eliminate the need for a Fan Mounted Accessory Gear Box (AGB) toprovide power to the BLI fan 108, may eliminate TBV, may enable electricanti-ice and Environmental Control System (ECS) and may provide animproved alternative for engine re-light by utilizing the BLI fan todrive associated generators.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A gas-electric propulsion system for an aircraft,the system comprising: a pair of jet engines suspended beneath a wing ofthe aircraft; an electric powered boundary layer ingestion fan fixedlyconnected to a fuselage portion of the aircraft aft of a tail section;and an electric generator coupled to at least one of the pair of jetengines and to the boundary layer ingestion fan, wherein the electricgenerator converts rotational energy from at least one jet engine of thepair of jet engines to electrical energy; wherein the boundary layeringestion fan is powered only by the electrical energy generated by theelectric generator; and wherein the boundary layer ingestion fan isconfigured to provide sufficient thrust to independently propel theaircraft.
 2. The system as in claim 1, wherein each jet engine of thepair of jet engines is a high-bypass ratio turbofan jet engine.
 3. Thesystem as in claim 2, wherein the high-bypass ratio turbofan jet enginesinclude a fan section having a plurality of fan blades, wherein the fanblades are variable or fixed pitch.
 4. The system as in claim 2, whereinthe high-bypass ratio turbofan jet engines are at least one of geared ordirect drive.
 5. The system as in claim 1, wherein the boundary layeringestion fan includes an electric motor electronically coupled to theelectric generator.
 6. The system as in claim 5, wherein the electricmotor is a superconductivity electric motor.
 7. The system as in claim1, wherein the electric generator is a high pressure electric generatorand is coupled to a high pressure spool of at least one jet engine ofthe pair of jet engines.
 8. The system as in claim 1, wherein theelectric generator is a low pressure electric generator and is coupledto a low pressure spool of at least one jet engine of the pair of jetengines.
 9. The system as in claim 1, further comprising an energystorage device electronically coupled to the electric generator and tothe boundary layer ingestion fan.
 10. The system as in claim 1, whereinthe system further includes an energy storage device electronicallycoupled to the electric generator and to the boundary layer ingestionfan, wherein the energy management system is electronically coupled toone or more of the pair of jet engines, the electric generator, theboundary layer ingestion fan and the energy storage device.
 11. Agas-electric propulsion system for an aircraft, the system comprising: aturbofan jet engine; an electric powered boundary layer ingestion fancoupled to a fuselage portion of the aircraft, wherein the boundarylayer ingestion fan is coupled to the fuselage downstream from a tailsection of the aircraft; and an electric generator coupled to theturbofan jet engine and to the boundary layer ingestion fan, wherein theelectric generator converts rotational energy from the turbofan jetengine to electrical energy; wherein the boundary layer ingestion fan ispowered only by the electrical energy generated by the electricgenerator; and wherein the boundary layer ingestion fan is configured toprovide sufficient thrust to independently propel the aircraft.
 12. Thesystem as in claim 11, wherein the turbofan jet engine is a high-bypassratio turbofan jet engine which includes a fan section having aplurality of fan blades, wherein the fan blades are variable or fixedpitch.
 13. The system as in claim 12, wherein the high-bypass ratioturbofan jet engine is one of a geared or direct drive turbofan jetengine.
 14. The system as in claim 11, wherein the boundary layeringestion fan includes an electric motor electronically coupled to theelectric generator.
 15. The system as in claim 14, wherein the electricmotor is a superconductivity electric motor.
 16. The system as in claim11, wherein the electric generator is a high pressure electric generatorand is coupled to a high pressure spool of the turbofan jet engine. 17.The system as in claim 11, wherein the electric generator is a lowpressure electric generator and it coupled to a low pressure spool ofthe turbofan jet engine.
 18. The system as in claim 11, furthercomprising an energy storage device electronically coupled to theelectric generator and to the boundary layer ingestion fan.
 19. Thesystem as in claim 18, wherein the energy storage device comprisesbatteries.
 20. The system as in claim 11 wherein the system furtherincludes an energy storage device electronically coupled to the electricgenerator and to the boundary layer ingestion fan, wherein the energymanagement system is electronically coupled to one or more of a pair ofjet engines, the electric generator, the boundary layer ingestion fanand the energy storage device.
 21. The system as in claim 1, wherein aninlet of the electric powered boundary layer ingestion fan is orientedwith respect to the fuselage to ingest at least a portion of a boundarylayer flow of air that is formed along the outer surface of the fuselageduring flight.
 22. The system as in claim 11, wherein an inlet of theboundary layer ingestion fan is oriented with respect to the fuselage toingest at least a portion of a boundary layer flow of air that is formedalong the skin of the fuselage during flight.
 23. The system as in claim1, further comprising an energy management system configured orprogrammed to monitor various system conditions.
 24. The system as inclaim 11, further comprising an energy management system configured orprogrammed to monitor various system conditions.